Especially in fields that use surface mounting technology or SMT for placing components on carriers, such as, e.g., blanks, solder connections between metallic terminal pins and soldering lands formed on a printed-circuit board or PCB are often used for forming mechanical and electrical connections.
Today, for providing the soldering lands, a metallic layer that is to be connected to the solder is deposited on circuit boards usually produced from plastic. Here, an adhesive bond between the circuit board and the solder is desired. However, because the galvanic layer deposited on the plastic by a PVD (Physical Vapor Deposition) method e.g., has low adhesive strength compared with the terminal pin on the solder e.g., it barely contributes to the mechanical strength of the solder connection.
The forces generated at an advancing solder edge can be calculated according to the equation from Young, i.e., according togSA=gLS+gLA cos θ  (1)wheregSA is the surface tension between the solid metallic workpiece layer (e.g., copper) and air,gLS is the surface tension between the liquid solder and solid metallic material layer, andgLA is the surface tension between the liquid solder and air and θ is the wetting angle that is a measure of the wettability of a material. In the case of θ=0°, a solder drop covers the metallic workpiece layer essentially as a single-molecule layer, while in the case of θ=180°, the liquid solder assumes the shape of a ball.